TY  - JOUR
A1  - Ratzloff, Jeffrey K.
A1  - Barlow, Brad N.
A1  - Kupfer, Thomas
A1  - Corcoran, Kyle A.
A1  - Geier, Stephan Alfred
A1  - Bauer, Evan
A1  - Corbett, Henry T.
A1  - Howard, Ward S.
A1  - Glazier, Amy
A1  - Law, Nicholas M.
T1  - EVR-CB-001: An Evolving, Progenitor, White Dwarf Compact Binary Discovered with the Evryscope
JF  - The astrophysical journal : an international review of spectroscopy and astronomical physics
N2  - We present EVR-CB-001, the discovery of a compact binary with an extremely low-mass (0.21 +/- 0.05M(circle dot)) helium core white dwarf progenitor (pre-He WD) and an unseen low-mass (0.32 +/- 0.06M(circle dot)) helium white dwarf (He WD) companion. He WDs are thought to evolve from the remnant helium-rich core of a main-sequence star stripped during the giant phase by a close companion. Low-mass He WDs are exotic objects (only about 0.2% of WDs are thought to be less than 0.3 M-circle dot), and are expected to be found in compact binaries. Pre-He WDs are even rarer, and occupy the intermediate phase after the core is stripped, but before the star becomes a fully degenerate WD and with a larger radius (approximate to 0.2R(circle dot)) than a typical WD. The primary component of EVR-CB-001 (the pre-He WD) was originally thought to be a hot subdwarf (sdB) star from its blue color and under-luminous magnitude, characteristic of sdBs. The mass, temperature (T-eff = 18,500 +/- 500 K), and surface gravity (log(g) = 4.96 +/- 0.04) solutions from this work are lower than values for typical hot subdwarfs. The primary is likely to be a post-red-giant branch, pre-He WD contracting into a He WD, and at a stage that places it nearest to sdBs on color-magnitude and T-eff-log(g) diagrams. EVR-CB-001 is expected to evolve into a fully double degenerate, compact system that should spin down and potentially evolve into a single hot subdwarf star. Single hot subdwarfs are observed, but progenitor systems have been elusive.
Y1  - 2019
U6  - https://doi.org/10.3847/1538-4357/ab3727
SN  - 0004-637X
SN  - 1538-4357
VL  - 883
IS  - 1
PB  - IOP Publ. Ltd.
CY  - Bristol
ER  -